1. Field of the Invention
The present invention relates to a raster scan display control apparatus. More particularly, the invention relates to such a display control apparatus for a display using a ferroelectric liquid crystal (FLC).
2. Related Background Art
Hitherto, in a raster scanning display control apparatus, the structure has been arranged to sequentially display image information, accumulated in a frame buffer, per line while keeping constant the displaying cycle for each of the scanning lines and the displaying cycle for one frame as well. Furthermore, if the frame frequency cannot be made high due to the material properties or electrical restraints of a display device, so-called interlace method is adopted to prevent flickers (screen flickering).
In a display device using a ferroelectric liquid crystal, particularly in case of a device having many numbers of lines, the use of a high order interlace (multi-interlacing) is imperative in order to prevent flickers.
However, if a display is performed by the use of the multi-interlacing, the object which is reproduced on a screen (for example, cursor, characters, icon, other graphics, or the like) is accompanied by so-called "barake" or dispersion when it is shifted or newly reproduced; hence spoiling the quality of display significantly. Particularly, a mouse cursor is directly operated by the user and its operational frequency is also high. Therefore, the dispersion attributable to the use of the mouse cursor may spoil the operational sensitivity of the entire system.
As means to prevent the dispersion of an object on a screen when multi-interlacing is applied, there is a method called "partial rewriting" such as proposed by Kanbe et al. (U.S. Pat. No. 4,655,561). This method is such that in shifting an object on a screen or reproducing it thereon, only the line area where the screen representation changes is temporarily displayed by non-interlacing method. There is also a method to implement this partial rewriting by means of software such as proposed by Inoue et al. (U.S. Pat. No. 5,058,994, U.S. Pat. No. 5,091,723, and others). However, no proposal has ever been made to regulate any particular means to be incorporated in the entire structure of a display control apparatus.